Method and apparatus to remove polluting components from the exhaust gases of internal combustion engines

ABSTRACT

Air and fuel are applied to the inlet manifold of an internal combustion engine over a first path, the amount of air being controlled in accordance with a command input, for example to control operation of the engine. The oxygen content in the exhaust gases is measured and additional air is applied to the inlet manifold of the engine over a second path, the amount of additional air being supplied over the second path being controlled in accordance with (a) the amount of air admitted through the first path and, additionally, (b) in accordance with the measured oxygen content of the exhaust gases.

United States Patent Wahl et a1.

[ Sept. 18, 1973 Robert Bosch GmbH, Gerlingen-Schillerhohe, GermanyFiled: June 23, 1972 Appl. No.: 265,547

Assignee:

Foreign Application Priority Data Jan. 29, 1972 Germany P 22 04 192.5

[5 6] References Cited UNITED STATES PATENTS 3,601,108 8/1971 Nambu123/119 ACCEL 3,698,371 10/1972 Mitsuyama 123/119 FOREIGN PATENTS ORAPPLICATIONS 600,895 4/1948 Great Britain 123/32 PrimaryExaminer-Laurence M. Goodridge Assistant ExaminerRonald B. CoxAttorneyFlynn & Frishauf Air and fuel are applied to the inlet manifoldof an internal combustion engine over a first path, the amount of airbeing controlled in accordance with a command input, for example tocontrol operation of the engine. The oxygen content in the exhaust gasesis measured and additional air is applied to the inlet manifold of theengine over a second path, the amount of additional air being suppliedover the second path being controlled in accordance with (a) the amountof air admitted through the first path and, additionally, (b) inaccordance with the measured oxygen content of the exhaust gases.

ABSTRACT 45 Claims, 13 Drawing Figures lCONTROL 25 AMP PREAMP FREQUENCYANLOG SIGNAL CONVERTER PATENTED 3,759,232

SHEEI 1 0F 4 \PRE-AM 43 FREQUENCY ANLOG SIGNAL n CONVERTER 1 25 cowgoL ABl -DIRECTIONAL Fl 9 2C1 SLIP ONE-WAY I I 35 CLUTCH 1 CLUTCH MOTOR Fig.2b 27 L flaw C-PD 1 35 23 4031 2 1. Q5 1.0.

PATENTEU 3.759.232

SHEET '4 BF 4 /I r l\ I 102 0 100 METHOD AND APPARATUS TO REMOVEPOLLUTING COMPONENTS FROM THE EXHAUST CASES OF INTERNAL COMBUSTIONENGINES The present invention relates to a method of removing pollutingcomponents from the exhaust gases of internal combustion engines, and toan internal combustion engine exhaust emission control system, theinvention being particularly applicable to internal combustion enginesof automotive vehicles.

Various methods and systems have been proposed in order to decrease theamount of polluting components in the exhaust of internal combustionengines, and particularly in automotive-type internal combustionengines. The oxygen content of the exhaust gases are measured by meansof an oxygen sensing device. Such an oxygen sensing device may be formedofa solid electrolyte, preferably zirconium dioxide, which is conductivefor oxygen ions. The output signal of the oxygen sensor then is appliedto a control amplifier to determine the position ofa bypass valve whichcontrols additional air being applied to the internal combustion engine.If insufficient oxygen is present in the exhaust gases, indicating thatthe mixture is too rich, additional air is provided by the bypass valveto provide a somewhat leaner air-fuel mixture to the engine.

Reference in the specification will be made to the air number, denotedlambda (A). This air number A is a measure of the composition of theair-fuel mixture. The number A is proportional to the mass of air andfuel, and the value of this number A is one (A 1.0) ifa stoichiometricmixture is present. Under stoichiometric conditions, the mixture hassuch a composition that, in view of the chemical reactions, allhydrocarbons in the fuel can theoretically combine with the oxygen inthe air to provide complete combustion to carbon dioxide and water. Inactual practice, even with a stoichiometric mixture, unburnednon-combusted hydrocarbons and carbon monoxide are contained in theexhaust gases.

Processes previously proposed influence the position of a bypass valvein accordance with the output of the oxygen sensing device without,however, considering the relative changes of the composition of theair-fuel mixture when the amount of air passing through the main airduct to the engine is high. For example, when the throttle valve of anautomotive-type internal combustion engine is wide open, the relativechange in the air number A is not influenced nearly as much by change inthe position of a bypass throttle, than when the amount of air passingthrough the main air path is low. The composition of the air-fuelmixture can be controlled with respect to all positions of the throttleto a predetermined value since the control loop, including the oxygensensor, can completely close or completely open the bypass valve, thecontrol loop itself including the oxygen sensor being a closed loop. Ifthe amount of air passing through the main air path is large, then thetime lag between correct balance of the air-fuel mixture and sensing ofdeviation from a desired level may be substantial since relative changesin the air-fuel mixture as above referred to by control of the throttlevalve alone then become small.

It is an object of the present invention to improve the control of theexhaust emission gases of internal combustion engines and particularlyto decrease the delay time of the closed control loop by making theresponse time of the control loop dependent on the amount of air beingpassed through the intake manifold over the direct air path.

SUBJECT MATTER OF THE PRESENT INVENTION Briefly, the base position of abypass valve is made dependent on the throttle position of the main airpath, that is, of the main control throttle, the additional change ofthe bypass valve being controlled in dependence on sensed oxygencomponent of the exhaust gases.

By considering the change to be made in the bypass air not only basedalone on the sensed oxygen in the exhaust, but also based on the airflow to the engine, sudden increases in air flow to the engine willcause the simultaneous increase in air flow of the bypass valve. Anystill necessary corrections can then be carried out by a controlamplifier in a substantially shorter period of time than would berequired if the base position of the bypass valve were controlled onlyfrom the oxygen sensor alone. The position of the main throttle valveinfluences the rotational speed of the internal combustion engine which,in turn, influences the air flow through the intake manifold. Thisinteraction can, in accordance with the embodiment of the invention, beconsidered by making the base position of the bypass valve dependent onthe position of the main throttle which controls the speed of theinternal combustion engine.

Relative changes of the composition of the air-fuel mixture can bematched closely to relative changes of the output voltage of the oxygensensor if, in accordance with a further feature of the invention, thecon trol amplitude of the control amplifier which determines theposition of an auxiliary throttle controlling bypass air operates independence on the throttle position of the main throttle and further ofthe speed of the internal combustion engine. By thus controlling thecontrol signal level, the control loop will respond with even lessdelay.

The invention will be described by way of example with reference to theaccompanying drawings, wherein:

FIG. 1 is a highly schematic representation of an internal combustionengine having a control loop in accordance with the present invention;

FIG. 2a is a schematic representation of one embodiment of a controlsystem for a bypass valve;

FIG. 2b is a schematic representation of a control loop for use in thesystem of FIG. 2a;

FIG. 3 is a schematic diagram ofa portion of the control loop of FIG.2b;

FIG. 4a is a schematic, cross-sectional view of a sensing element;

FIG. 4b is a graph illustrating operation of the sensor of FIG. 40;

FIG. 5 is a block diagram of a different embodiment of the control loop;

FIGS. 6 to 8 are cross-sectional views of different types of bypassvalves, and their control, in which FIG. 8b is a detail of the valve ofFIG. 8a;

FIG. 9 is a schematic diagram of another form of the control loop; and

FIG. 10 is a fragmentary cross-sectional view of another embodiment of abypass valve.

The internal combustion engine 11, shown for purposes of thisapplication as a four-cylinder engine, although it may be any type ofinternal combustion engine, and not restricted to a reciprocating-typeinternal combustion engine, has intake air delivered over an air filter12 connected to an intake duct 13. Throttle 14 is movably located withinduct 13, the throttle being operatecl from a control pedal 30. Thenozzle 15, shown schematically only, of a carburetor delivers fuel fromfuel supply 16.

Filtered air is additionally supplied to the internal combustion engineover a bypass duct 17, which bridges the carburetor nozzle 15. In theembodiment shown, the bypass air is taken through the air filter 12,then branches off from inlet duct 13 and terminates behind throttle 14at the engine side of duct 13. The amount of air passing through thebypass 17 can be controlled by means ofa bypass valve 18. Bypass valve18 is electrically controlled, and is connected to the output of acontrol amplifier 25. Bypass valve 18 may, additionally, be setmechanically by connection from the accelerator pedal 30, asschematically indicated by the dashed line in FIG. 1.

The exhaust from the internal combustion engine 11 is connected to amanifold 19, the wall 20 of which is thermally insulated with respect tosurrounding air. The manifold 19 terminates in a catalytic reactor 21and the output from the catalytic reactor is then connected to anexhaust pipe, muffler, and the like, conjointly schematically indicatedat 22.

An oxygen sensing element 23 is located in the wall 20 of the exhaustmanifold 19, or its exhaust duct. The electrical output of the oxygensensor 23 is connected to a pre-amplifier 24 and, after amplification,to one input of the control amplifier 25. The shaft of the internalcombustion engine drives a tachometer generator which, for example, mayconsist of a series connection of a pulse source 32 and a frequencyresponsive direct current output converter circuit 33, operating as adigital-analog converter and converting the output of pulse source 32which has a frequency representative of engine speed into a directcurrent voltage likewise representative of engine speed. The outlt ofconverter 33 is connected to a second input of the control amplifier 25.

The accelerator or control pedal is further connected to aposition-current transducer 31 which may, in its simplest form, bemerely a potentiometer connected with one terminal to a source ofreference voltage and on the other to chassis, so that upon change ofthe position ofpedal 30, the tap point of the potentiom eter willlikewise change. The output voltage of the position transducer 31 isproportional to the deflection angle of the pedal 30, and connected to athird input of control amplifier 25.

The mechanical arrangement to control the bypass valve 18 isillustrated, highly schematically, in FIG. 2a. The throttle 14 issecured to a throttle shaft 34; the throttle shaft 34 additionallydrives the movable contact of a potentiometer 31, the output terminalsof which are connected between a reference source and chassis. Apositioning motor 35 is connected to a slip coupling 37 ofa bypass valveshaft 29 which carries the bypass throttle disk 18. Potentiometer 36,connected between a reference source, indicated as terminal 40 andchassis provides an output signal representative of the angulardeflection of motor 35. A bi-directional one-way clutch, in the form ofa free-wheeling clutch 38 interconnects the bypass valve shaft 29 andthe throttle valve shaft 34. Clutch 38 is so arranged that it transfersmovement ofthe throttle valve shaft 34 to the bypass valve shaft 29 inboth rotary directions but blocks any feedback of movement from theshaft 29 to the throttle shaft 34.

The circuit according to FIG. 2 has the elements 23, 24, 25 and 31connected in the same way as in the schematic representation of FIG. 1.The control amplifier 25, however, is somewhat simpler, in that it doesnot have an input to connect an electrical representation of enginespeed, that is, the output from the frequencyanalog converter 33 is notrequired. A second input 27 of control amplifier 25 is used to introducea command value representative of the air number k, that is, theproportion of the air and fuel mixture. Control amplifier 25 isconnected to a servo amplifier 39, providing an output voltage tooperate the positioning motor 35, and having error input connected tothe tap point of the positioning potentiometer 36, as well known inservo technology.

The details of the control amplifier 25 are illustrated in FIG. 3 and,essentially, includes an integral controller, utilizing an integratingoperational amplifier 250. The output of operational amplifier 250 isconnected over resistor 252 with positive reference terminal 40'. Thenon-inverting input of the operational amplifier 250 is connected overan input resistor 254 to the tap point of a voltage divider formed ofresistors 255, 256. The feedback connection of the operational amplifier250 includes an integrating condenser 251.

The inverting input of operational amplifier 250 is connected overcoupling resistor 253 with the collector electrodes of a pair oftransistors 257, 258, the transistors being of opposite conductivitytype. The emitter of the npn transistor 257 is connected to the input ofan inverting amplifier 261 which, in turn, connects to the emitter ofthe pnp transistor 258. Further, the input of amplifier 261 and emitterof transistor 257 is connected to the tap point of potentiometer 31which forms the position transducer for control pedal 30.

The pre-amplifier 24, connected to the output of sensing element 23, isconnected over an input transistor 265 to the inverting input of anoperational amplifier 262. the non-inverting input is connected overfeedback resistor 263 with the output of the operational amplifier and,further, over a coupling condenser to the tap point of a voltage dividerformed of resistors 267, 268, of which resistor 267 is adjustable. Theoperational amplifier 262 functions as a threshold switch, thesensitivity or response threshold of which is adjustable by setting theresistor 267. The tap point between the two resistors 267, 268 forms theinput terminal 27 (FIG. 2b) of reference voltage, to provide a commandvalue, adjustable by resistor 267. The output of the operationalamplifier 262 is connected over coupling resistor 264 to the positivesupply bus 40 and, further, over resistors 259, 260 to the base terminalof the transistors 257, 258, respectively.

The oxygen sensor FIG. 4a is essentially composed of a closed tube 42including a sintered solid electrolyte. The tube 42 has a platinum layer43 with micropores formed therein, the platinum layer being applied, forexample, by vapor deposition. The two platinum layers 43 are suppliedwith electrical terminals which are connected to terminal connections44,

45. Tube 42 is inserted in a socket 41 and located in the wall of theexhaust gas, or exhaust manifold. Socket 21 is formed with a borethrough which ambient outside air can penetrate into the interior of theclosed tube 42. The outer surface of tube 42 is exposed to the exhuastgases.

FIG. 4b is drawn with respct to the air number A which has a value ofone when a stoichiometric air-fuel mixture is present, and defines theratio of mass of air to fuel; for perfect combustion of gasoline thisratio is usually in the order of about 14.4 1. If the mixture is lean,then the air number A is greater than one; rich mixtures are representedby air numbers less than one.

The output voltage of the sensor 23 is illustrated in FIG. 4 withrespect to the air number A. The solid electrolyte, at the temperaturesusually present in the exhaust stream, is oxygen-conductive. A suitablesolid electrolyte may be zircoium dioxide. When the oxygen partialpressure of the exhaust gases departs from the oxygen partial pressureof ambient air, then a voltage difference will arise between theterminals 44, 45. This voltage difference is illustrated, with respectto the air number A, by curve 46 in FIG. 4b, and depends,logarithmically, of the quotient of oxygen partial pressure present atboth sides of the solid electrolyte 42. The output voltage of the oxygensensor thus changes rapidly in the vicinity of an air number A 1.0.Above A 1.0, unburned oxygen will be present in the exhaust gases; dueto the substantial dependence of output voltage of the sensor from theair number A, the oxygen sensor as referred to in FIG. 4a (and see alsothe cross referenced applications) is particularly suitable to controlthe system.

Method of controlling exhaust emission, and operation of the system:Catalytic reactor 21 is designed to reduce nitrogen oxide components,primarily NO and N0 These components can be reduced only when theexhaust gases have a slightly reducing composition. The air number Athus must be controlled at all times to be just below a value of 1.0. Asthe air number A drops below 1.0, more carbon monoxide and unburnedhydrocarbons will be contained in the exhaust gases. It is thusdesirable to control the air number to have a value of, for example,0.98 which is high enough so that only very little unburned hydrocarbonsand carbon monoxide are present in the exhaust gas but yet stillprovides a reducing atmosphere. The thermal reactor which is immediatelyconnected to the outlet valves, and formed essentially by the thermallyinsulated exhaust manifold 19 serves as an after-burner for unburnedhydrocarbons and for carbon monoxide. FIG. 1 illustrates this thermalreactor only schematically. Due to thermal isolation, the wall of theexhaust manifold 19 will reach a temperature of from between about 600to 800 C, which is sufficient to start afterburning of the combustiongases from the internal combustion engine. It is also possible toutilize a more complicated, separate thermal or thermo reactor forafter-burning, without departing from the inventive concept.

The inventive concept may also be used without the catalytic reactor 21if elimination of nitrogen-oxygen compounds is not required although ahigher percentage of nitrogen oxygen compounds will then be present inthe total exhaust emitted from the engine. 7

The system of FIG. 2a changes the bypass throttle 18, used here insteadof a separate bypass valve. The base position of throttle 18 isdetermined by the position of throttle shaft 34, the position of whichis transmitted over the one-way clutch 38. If throttle 14 changes, forexample in opening direction, bypass throttle blade I8 is turned overthe one-way clutch, likewise, to an open ing direction. In certaininstallations, the one-way transmission 38 may be combined with astep-down gearing, or a step-down lever arrangement, so that the bypassflap 18 rotates over a smaller angle than the valve 14. The positioningmotor does not rotate upon change of position of the bypass valve 18,since the slip clutch 37 well merely run free.

If the oxygen sensor 23 provides an output signal which indicates adeviation from the air number A 0.98, then the servo amplifier 39 (FIG.2b) will become energized to energize motor 35 to rotate in theappropriate direction. The slip clutch 37 will transmit rotation fromthe rotor 35 to the shaft 29 and hence to the bypass throttle 18. Themain throttle 14 does not, however, change its position since theone-way clutch 38 will not transmit rotary movement from shaft 29 to thethrottle shaft 34.

Servo amplifier 39 is a power amplifier which is so connected that itsoutput provides a positive supply voltage for the motor 35 when theoutput voltage of control amplifier 25 is more positive than the voltagesupplied from the position sensor 36. Such positive output voltage ofthe servo amplifier 39 causes the motor 35 to turn to the left (FIG 2b),which rotary motion will continue until the output voltage of theangular position transducer 36 will match the value of the outputvoltage of the control amplifier 25, so that the error signal becomeszero, in accordance with well known servo techniques. At that condition,servo amplifier 39 will no longer supply power to motor 35 and motor 35will stop. If the output voltage of the control amplifier 25 has a valuewhich is negative with respect to the-voltage of the position transducer36, then a negative supply voltage will be applied to the motor whichwill then turn towards the right until the voltages again balance.

Let it be assumed that the bypass valve 18, due to a base postion of theclutch 38, has turned too far. Under this condition, the air number Awill become too great and the oxygen sensor 23 will provide a low outputvoltage which is pre-amplifier 24. The output voltage supplied bypre-amplifier 24 is less than the voltage at terminal 27 (FIG. 2b; FIG.3). The threshold switch formed of operational amplifier 262 andfeedback resistor 263 will provide an output voltage which will be closeto that of the positive bus 40, which output voltage will be appliedover resistor 259 to transistor 257 which will become conductive. Thepositive output voltage of potentiometer 31, which is the positiontransducer for the accelerator pedal 30, is applied to the intput'ofoperational amplifier 250. Integrator 250, 251 integrates in negativedirection, and the servo amplifier 39 will provide a negative supplyvoltage to the positioning motor 35 so that it will then turn to theright. This rotation to the right changes the position of the bypassthrottle 18 (FIG. 2a) in such a direction that only a smaller crosssection will be available in bypass tube 17 for air to passtherethrough.

Whn the bypass throttle 18 has been sufficiently displaced, so that theadditional air stream has decreased, the air number A will drop andreach, for example, the value 0.98. At that position, the oxygen sensor23 provides a sharply higher output voltage. The output voltage at thepreamplifier 24 will exceed the voltage at terminal 27 (FIG. 2b, FIG. 3)so that the output of operational amplifier 262 will jump to negative,or chassis voltage. This negative voltage will block the previouslyconductive transistor 257 and open the previously blocked transistor258. The inverter amplifier 261 provides an inversion, that is, anamplification of v l and, thus, provides inverted output voltageproportional to the voltage at the tap point of the position transducer31. The inverting input of the operational amplifier now has negativeinput voltage applied thereto, depending on the position of theaccelerator pedal 30. The operational amplifier 250 will integrate inpositive direction and the servo amplifier 39 provides an output voltagecausing rotation of motor 35 to the left, to cause opening of the bypassvalve 18.

As seen from the above, the output voltage of the oxygen sensor 23controls the threshold switch (operational amplifier 262 with itsfeedback resistor 263) only to set the direction into which the outputvoltage of integrator 250, 251 will slowly change. The output voltage ofthe position transducer 21 determines the speed with which the outputvoltage of integrator 250, 251 changes. If the main throttle 14 is wideopen, high positive or negative input will be applied to integrator 250,251, so that the output voltage of the operational amplifier 250 willchange rapidly in negative or positive direction, respectively. Thisshift is much slower when the throttle 14 is only slightly open, so thatthe input voltage applied to the inverting input of the operationalamplifier is low. The object of the control system, above referred to,is thus achieved: When a large quantity of air passes through the inletmanifold, that is, when the main throttle 14 is wide open, the bypassthrottle 18 changes position rapidly. The relative change in thequantity of air passing therethrough in a predetermined time interval,and thus the air number A is kept constant for all possible positions ofthe main throttle 14.

The control loop is stable under all operating conditions since the timedelay is matched to the air flow. It would be theoretically possible toutilize a proportional controller rather than the integral controller250, 251, which has a very low delay time in comparison to the timedelay of an integral controller. This, however, is undesirable for tworeasons: First, the integral controller will effectively compensate forremaining control deviations, for example due to drift, aging of thesensor and subsequent changes in output voltages of the sensor, and thelike; and further, since the output curve 46 in the region of the airnumber A 1.0 is very steep, a proportional controller might change thebypass throttle rapidly either too far, or to effect closing of thebypass throttle 18 too much.

The base position of the bypass valve 18 can be changed mechanically, asillustrated in connection with FIGS. 2 and 3. The output voltage of theoxygen sensor 23 determines the direction into which the bypass throttle18 is to be changed; the operating speed is determined by the mainthrottle position 14. Under certain conditions it is desirable to changethe operating speed not based on main throttle position but rather inaccordance with engine speed. The circuit of FIG. 3 can easily bemodified if, instead of the position transducer 31 being connected toinverting amplifier 261 and to the transistor 257 (FIG. 3), a digitald-c analog converter such as the frequency-analog signal converter 33 isconnected to terminal 3] (FIG. 3). It is of course also possible tochange the positioning speed of the bypass throttle 18 in dependence onboth the main throttle position 14 (that is, of the control pedal 30)and the motor speed as well. In this instance, the terminal 31 will havea summing circuit applied thereto as illustrated, for example, in FIG.3, which includes summing resistors 50, 51, 52 and an operationalamplifier 53 with a feedback resistor 54. By suitable selection anddimensioning of the summing resistances corresponding to resistors 51,52, and to which position transducer 31 and the frequency-analog signalconverter is connected, the operating speed of the bypass throttle 18can be changed in accordance with desired relationships of the inputvalues affecting the position of the bypass throttle. Changing the valueof resistance of the trimmer resistor 267 changes the threshold value ofthe air number A which, in the above described example, is set to avalue of 0.98.

The system of FIG. 2a, can likewise be changed by eliminating themechanical base position of the bypass valve 18 over the one-way clutch38, since the base position can equally be controlled electrically. Inthis instance, the servo amplifier 39 has control voltages appliedthereto which include the output voltage of the control amplifier 25,the position transducer 31, and the frequency-analog signal converter25, if desired. Such an electrical system for basically setting thebypass valve 18 in dependence on the position of the main valve 14 isdescribed in more detail in FIG. 5; for correspondence, it is onlynecessary to utilize a servo amplifier 39 rather than the operationalamplifier 53, in the output, as illustrated and described in accordancewith FIG. 5.

A modified control circuit is illustrated in FIG. 5 to carry out themethod of the present invention. The control amplifier 25 has an inputterminal 27, to which a command value is applied. A second input ofcontrol amplifier 25 is connected to the output of pre-amplifier 24. Thethird input of control amplifier 25 has the output of the positiontransducer 31 applied thereto. The output of the control system of FIG.5 is applied to a magnet or solenoid coil 55 which controls a valveposition. An operational amplifier 53, with a feedback resistor 54, hasan inverting power amplifier 56 connected to its output, to drive thesolenoid coil 55. The operational amplifier 53 operates as aproportional amplifier; its non-inverting input is connected to areference potential, for example to the tap point of a voltage divider,not shown. The inverting input of the operational amplifier is connectedto three adding resistors 50, 51, 52 which, respectively, have theoutput voltages of control amplifier 25, position transducer 31, and thefrequency-analog signal converter 33 applied thereto.

FIGS. 6, 7, and 8 show various embodiments of bypass valves which can becontrolled by the circuit of FIG. 5, and which have magnetic coilscorresponding, in operation, to the load coil 55 of FIG. 5.

In accordance with FIG. 6, an inlet opening 60 is connected over valveseat 62 to an outlet opening 61; the valve seat 62 can beproportionately opened or closed by a valve cone 63 which is guided bymeans of rod 66 in a bore 72 of the valve housing 65. Cone 63 isspringloaded by a spring 64. A cup-shaped magnet 69, which is apermanent magnet, is attached to housing 65. The cup magnet has acylindrical south pole 71 and a ringshaped north pole 70,circumferentially surrounding south pole 71. North pole 70 has one ofits faces profiled, as seen at 73, for example by removing of metal on alathe, so that the air gap of the magnet 69 has a non-linearcharacteristic. coil 68 enters into the air gap, the coil being securedto a base plate 67 attached to guide rod 66. Coil 68 is supplied withcurrent over two pigtails brought out to terminal 74, 75.

The bypass valve of FIG. 7 has a similar air control section to that ofFIG. 6; it differs in the electromagnetic structure. The cup-shapedmagnet is an electromagnet which is energized coil 78, wound on thecylidrical pole extension of magnet 70. A pair of supply terminals 79,80 connect to coil 78. The guide rod 66' is longer than guide rod 66(FIG. 6) and extends into a cylindrical bore within the center portionof the magnet 70. An armature 76 is connected to the guide rod 66between the valve housing 65 and the cylindrical center pole of themagnet. The armature 76 has a facet 77 removed, so that the air gapbetween the ringshaped magnetic pole 70 and the armature 76, uponmovement of the armature 76 into the air gap, will be somewhatnon-linear.

The bypass valve of FIG. 80 has a valve structure which is similar tothat previously described with the exception, however, that the valvecone 63 has a nonlinear contour so that the air stream passing throughthe valve seat 62, when the valve cone is lifted off the seat 62, willbe non-linear with respect to travel of the cone 63,. Only smallmechanical forces are necessary to deflect the valve cone 63 of thevalve of FIG. 8a. The guide rod 66, therefore, is not retained infriction bearings but rather is held by means of a pair of leaf springs85, 86 (FIG. 8b) which are connected directly to projections 83, 84 ofthe valve housing 65. Holes 87 in leaf springs 85, 86 connect the leafsprings to the projections 83, 84; the central opening 88 accepts thecentral guide rod 66. The sring, as best seen in FIG. 8b, has a highdegree of stiffness in radial direction but can readily deflect in axialdirection, where its stiffness is low. Thus, only very small positioningforces are necessary to move the guide rod 66, and with it cone 63, inlongitudinal direction.

The space between the valve seat 62 and the outlet opening 61 is sealedby a membrane 82, so that the electromagnetic structure is sealed withrespect to the pneumatic structure of the valve. The membrane 82 isconnected in gastight relation to the guide rod 66 and to the housing 65of the valve. A central bore 81 interconnects the air spaces between themagnet and the valve, to provide for pressure equalization. The pressureequalization permits use of even smaller positioning forces; yet, theflow resistance of a long, very thin bore 81 is so high thatoscillations of the mechanical 7 system formed by the guide rod 66 andthe pressure spring 64 are well damped.

The electromagnetic structure of the valve of FIG. 8a is not shown,since either structure above discussed in connection with FIG. 6 or FIG.7, or equivalent and alternative structures can be used.

Operation of system of FIG. in connection with valves of FIGS. 6 to 8:The bypass valves, FIGS. 6-8, are opened wider when the control currentderived from the circuit of FIG. 5 increases, that is, when the currentapplied to terminals 74 or 79, 80, respectively, increases. The baseposition of the bypass valve is obtained electrically, not by mechanicalmeans as described in connection with the example of FIGS. 1-3. Theoutput voltages of the position transducer 31, the

III

frequency analog transducer 33 and the sensor are all applied to theoperational amplifier 53 and the power amplifier 56. The output voltageof converter 33 increases with output frequency of the pulse source 32,that is, with speed of the internal combustion engine. The outputvoltage of the position transducer 31 increases with increasing openingof the main throttle valve 14 (FIG. I). Since the operational amplifier53 is controlled by the inverting input, and power amplifier 56 islikewise inverting, the current applied to the magnetic coil 55(corresponding to coil 68 FIG. 6 or 78 FIG. 7) will increase withincreasing input voltage of the operational amplifier 53.

As described in connection with the first example, the base position ofthe main valve 14, as determined by the position transducer 31,influences the position of the bypass throttle 18. Further, the speed ofthe internal combustion engine is used as an additional factor to changethe base position. Thus, the base position of the bypass valve ismatched well to the actual air mass passing through the main air pathinto the intake manifold 12'. This base position is added to theadditional control determined by the output signal of the controlamplifier 25.

Operation: Let it be assumed, to illustrate a specific control cycle,that bypass valve 18 has been opened too far, due to control from thebase position. This causes an increase in the air number A which will gobeyond the set value, and the oxygen sensor will supply a low outputvoltage (see FIG. 412). As described in connection with the circuit ofFIG. 3, operational amplifier 250 will integrate in negative direction.The input voltage of the operational amplifier 53 is thereby decreased,due to the application of this decreasing value over summing resistor50, and excitation current for the magnet winding 55 (that is, for coils68, 78) will decrease. Bypass valve 18 will close more; it will continueto close until air number A has decreased to the point at which theoutput voltage of the oxygen sensor 23 exceeds the threshold limit ofthe threshold switch formed by operational amplifier 262, 263 and, uponresponse of operational amplifier 262, 263, integration will thenproceed in opposite direction. Change-over of the threshold switch 262,263 indicates that the air-fuel mixture has become too rich, andexcitation current to the magnetic winding is increased to permit thevalve to open more.

The actual control cycle is thus similar to that of the initiallydescribed example. The difference essentially resides in the fact thatthe base position is electrically obtained. By suitable choice of therelative values of the adding resistors 50, 51, 52, it is possible tochange the control excursion and control limit of e operationalamplifier 53, and hence of the power amplifier 56. The contours orprofiles 73 (FIG. 6) and 77 (FIG. 7) or the shape of the cone 63' (FIG.8a) can be utilized additionally to compensate for non-linearities inthe control loop.

A further embodiment illustrated in FIG. 9. The requirement forelectrical components of the system of FIG. 9 is less than that of theprevious systems, however, the mechanical requirement for components isincreased. Both bypass valves of FIGS. 6, 7, can be combined, byconnecting a coil 68 mechanically with the pin or rod 66 and forming,additionally, the magnet in which the coil operates as an electromagnetwith its own magnetic winding 78. The connection of such a system isillustrated in FIG. 9, where the movable coil is schematically indicatedat 97 and the excitation winding for the magnet at 98. Both windings 97,98 have power amplifiers 95, 96, respectively, connected thereto. Theposition transducer 31 and the speedanalog converter 33 are connectedover adding resistors 91 to 94 with the inputs of the two poweramplifiers 95, 96. The output of control amplifier 25 is furtherconnected over an additional adding resistor 90 to the input of thepower amplifier 95. In this form of the invention, the control loop ofthe control amplifier 25 is an integral controller without contol of thetime constant thereof. The oxygen sensor 23 again has preamplifier 24connected thereto which, in this instance, is an inverting-typeamplifier, to provide a signal polarity reversal. An operationalamplifier 250 is used as integral controller, as in the first example inaccordance with FIG 3, connected with an integrating capacitor 251 inits feedback path. The noninverting input is connected to a source ofcontrol voltage formed by the tap point of voltage divider resistors255, 256, resistor 255 being adjustable. The tap point is connected overcoupling resistor 254 and the output of inverting-type preamplifyingamplifier 24 is connected over a coupling resistor 253.

The basic position of the bypass valve 18 changes with the position ofthe main valve 14 (FIG. 1), as in the second example, under electriccontrol. The output voltages of the position transducer 31 and of thefrequency-direct current analog converter 33 are added at the inputs ofthe two power amplifiers 95, 96, so that the base position is applied asa positioning value both to the movable coil 97 as well as to theexcitation winding 98. By suitable choice of the resistances of theadding resistors 91 to 94, any desired non-linear function orrelationship may be commanded, so that nonlinearities in the controlloop can be corrected. The additional change in positon, depending onoutput gas composition is obtained by applying a signal over adderresistor 90 which nfluences only the movable coil 97. In operation, thecontrol system operates as in the previously discussed example. When theair number x is too great, oxygen sensor 23 provides a low voltage whichis amplified in the pre-amplifier 24 to provide, due to its invertingcharacteristic, a high output volt- I age. Integrator 250, 251 thusintegrates in negative direction. The coil 97 has less current appliedthereto from amplifier 95 and bypass valve 18 will move in closingdirection.

The control amplifier of FIG. 9 may be similar to that of FIG. 3, whichwill additionally cause the positioning speed of the bypass valve 18 tobe controlled. It is also possible to control the output of amplifier 25to the power amplifier 96 rather than to amplifier 95, as shown.

FIG. illustrates a further embodiment of a bypass valve which, as inFIGS. 6 to 8, has an inlet opening and an outlet opening 61. The valvecone 63 is guided over rod 66 in a bore 72 of housing 65, and biassed toclosing position by means of a spring 64. The bypass valve of FIG. 10,similar to the bypass disk valve 18 of FIG. 2a, has a mechanical inputto influence its base position. This mechanical input is a movable valveseat 100, movably retained within the valve housing. Valve seat 100 isformed with a lateral opening 101, in which a earn 102 may move, toshift the position of valve seat 100 left to right referring to FIG. 10depending on position of the cam. The valve seat itself is biassedtowards the right by spring 103, which is located between valve seat 100and housing 65.

Carn 102 is mechanically connected with the throttle 5 shaft 34 (FIG.2a). Upon movement of the throttle shaft 34, valve seat 100 will move.By suitable shaping of the cam 102, or of the opening 101, or both,nonlinear relationships between base position of the main throttle valve14 and of the bypass valve can be obtained. The valve cone 63 may beshaped with a contour which is non-linear, for example similar to thatof valve cone 63' (FIG. 8a). Thus, by simple mechanical shaping,non-linearities in the control loop can be compensated. The pin 66 canbe controlled in position as discussed in connection with theembodiments of FIGS. 6 or 7, by means of a coil, an armature, by bothor, separately, as discussed in connection with FIG. 9.

The method in accordance with the present invention thus providescontrol of bypass air to an internal combustion engine which depends onboth the position of the main throttle valve, as well as other operatingparameters of the engine that is, in this example, primarily exhaust gascomposition and engine speed. Other parameters can be utilized to affectvalve position, by connecting further summing resistors to the controlcircuits, similar to resistors 90, and 91-94 (FIG. 9) or St), 51, 52(FIG. 5), for example. The base position of the main throttle valve 14thus controls the opening of the bypass valve 18, and this setting isfurther matched to the speed of the internal combustion engine 11. Atany air flow, the relative change of the air number A will thus changein dependence on the output signal of the oxygen sensor 23. Both thecontrol limits, that is, the control range and the delay time of thecontrol amplfier can be matched to the air flow to the engine. Thus,rapid changes in operating conditions of the internal combustion enginescan be followed, so that, upon fast, large changes, the controlamplifier will respond rapidly.

Various changes and modifications may be made within the inventiveconcept.

We claim: 1. Method to remove polluting components from the exhaustgases of internal combustion engines comprismg applying an air-fuelmixture to the inlet manifold (12') of the engine (11) over a first path(13);

controlling (M) the relative proportion of air and fuel in the air-fuelmixture being admitted through said first path, in accordance with acommanded input measuring the oxygen content (23) of the exhaust gasesfrom the engine;

applying air to the inlet manifold (12) of the engine (11) over a secondpath (17); and controling (18) the amount of air being admitted throughthe second path in accordance with a. the amount of air being admittedthrough the first path and, additionally, b. the measured oxygen contentof the exhaust gases.

2. Method according to claim 1 wherein the step of controlling theamount of air being admitted through 5 the first path (13) comprisessetting a throttle valve (14) in the main air duct in accordance with acommanded position; and the step of controlling the amount of air beingadmitted through the second path (17) comprises providing an auxiliaryair inlet duct (17), in shunt with the main air duct (14) and having anauxiliry valve (18);

and controlling the position of the auxiliary valve (18) in accordancewith the position of the main throttle valve (14) as modified by themeasured oxygen content of the exhaust gases.

3. Method according to claim 1, wherein the step of controlling theamount of air being admitted through the second path comprisesadditionally controlling the amount of air being admitted as a functionof engine speed.

4. Method according to claim 1, wherein a control amplifier (25) isprovided, and electrically controlled air flow means are provided insaid second path, the output of the control amplifier controlling theair flow control means in the second path to effect the step ofcontrolling the amount of air flowing through the second path;

and wherein the range of output of the control amplifier (25) iscontrolled by at least one of the parameters: engine speed; air flow inthe first path.

5. Method according to claim 4, wherein the control amplifier (25) has avariable delay time; I

and the delay between control input to the control amplifier and thecontrol output thereof is varied in accordance with at least one of theparameters: engine speed; air flow in the first path.

6. Method according to claim 1, wherein the air flow in the second path(17) is controlled such that the relationship of air mass to fuel beingsupplied at the inlet manifold (12) to the engine is just below thestoichiometric ratio and has a value of about 0.98.

7. Method according to claim 5, comprising the step of after-burningunburned carbon monoxide and hydrocarbons in a thermo reactor (19, 20),and then reducing nitrogen-oxygen compounds in a catalytic reactor (21)following the thermo reactor.

8. Internal combustion engine exhaust emission cleaning system, in whichthe internal combustion engine (11) has an inlet manifold (12),

means (15) introducing fuel into the inlet manifold;

means (14) controlling the flow of air in the inlet manifold in a firstpath; means (17) introducing additional air into the inlet manifold in asecond path;

means (18) controlling the flow of additional air into the inletmanifold through an additional air path;

exhaust gas analysis means (23) measuring the oxygen content of theexhaust gases and deriving an electrical sensing signal;

and electromechanical control means connected to and controlling theflow control means for the additional air, the electromechanical controlmeans having an input which is responsive to the amount of air flowingin the first path and further to said electrical sensing signal tocontrol the flow of additional air as a function of the flow of air inthe first path as well as a function of a predetermined relationship ofoxygen in the exhaust gas as sensed by said exhaust gas analysis means(23).

9. System according to claim 8, wherein the internal combustion enginehas a settable control (30) including means (31) deriving a signalrepresentative of the position of said control and applying said signalto the electromechanical control means in a direction to increaseresponse time of said control means when the settable control is set forhigh power operation of the engine providing for high air flow throughsaid first path.

10. System according to claim 8, wherein the means controlling the flowof air in the first path comprises a main throttle valve (14) having ashaft (34);

the flow control means for the additional air path comprise anadditional throttle valve (18) having an additional shaft (29);

and the electro-mechanical control means comprises mechanical means (38,responsive to throttle shaft (34) deflection connected to operate theadditional throttle shaft (29) and additional electrical inputposition-output electrical signal transducer means (35) responsive tothe electrical sensing signal additionally deflecting the additionalthrottle valve (18).

11. System according to claim 10, wherein the mechanical means comprisesa bi-directional one-way clutch (38) connected at the driven side withthe main throttle shaft (34) and at the driving side to the additionalthrottle shaft (29) to transmit rotary movement from the throttle shaft,in both rotary directions, to the additional throttle shaft (29) but notto transmit rotary movement in either rotational direction from theadditional throttle shaft (29) to the main throttle shaft (34); and theelectrical input-position output transducer comprises a synchro motor(35) and a slip coupling (37) connecting the synchro motor to theadditional throttle shaft (29) to permit setting of the additionalthrottle (18) upon change in position of the main throttle shaft (34)and modifying this position under control of the operation of thesynchro motor.

12. System according to claim 11, further comprising a closed servo loop(35, 36-39) including a position transducer (36) coupled to the outputshaft of the synchro motor (35).

13. System according to claim 12, wherein the servo loop includes aservo amplifier (39) controlling the amount and direction of rotation ofthe synchro motor (35);

and means including a reference source (40) connected to the positiontransducer, the output from the position transducer forming a comparisoninput to the servo amplifier (39).

14. System according to claim 13, wherein the electro-mechanical controlmeans comprises a control amplifier (25) having an output connected toand controlling the servo amplifier (39);

a source of command signals representative of commanded fuel-air ratio,said control amplifier having one input connected to said command sourceand another input connected to the output of the gas analysis means.

15. System according to claim 12, further comprising a positiontransducer (31) coupled to the main throttle shaft (34) to provide asignal representative of main throttle shaft deflection.

16. System according to claim 14, further comprising a positiontransducer (31) coupled to the main control shaft (34) to provide asignal representatve of main throttle shaft deflection;

said control amplifier having a third input connected to the output ofthe position transducer (31).

17. System according to claim 14, wherein the control amplifier is anintegrating amplifier.

18. System according to claim 17, wherein the integrating amplifierincludes an operational amplifier (250) having an output and aninverting input;

and an integrating capacitor (251) connected between the output and theinverting input.

19. System according to claim 18, (FIG. 9), wherein the gas analysismeans (23) is interconnected with the inverting input of the operationalamplifier (250).

20. System according to claim 18, further comprising a positiontransducer (31) coupled to the main throttle shaft (34) to provide asignal representative of main throttle shaft deflection;

a first transistor (257) interconnecting the output of the positiontransducer (31) and the inverting input of the operational amplifier(250);

a series connection formed of an inverting amplifier (261) and a secondtransistor (258) connected in parallel to the first transistor;

said transistors being of opposite conductivity types.

21. System according to claim 20, further comprising a threshold switch(262, 263) connected to the gas analysis means (23), the output of thethreshold switch being connected to the base electrodes of the first andsecond transistors (257, 258).

22. System according to claim 21, wherein the threshold switch comprisesan operational amplifier (262) having a resistor (263) in the feedbackcircuit from the output to the non-inverting input thereof.

23. System according to claim 8, wherein the means (18) connecting theflow of additional air comprises a bypass valve having anelectro-mechanical positionable valve cone (63) and a mechanicallymovable valve seat (10 0);

and drive means (102) operatively interconnecting the means controllingflow of air in the first path and the mechanically movable valve seat tomove the valve seat in accordance with change in position of said flowcontrol means.

24. System according to claim 23, wherein the flow control means for thefirst path comprises a throttle and a throttle shaft and the drive meanscomprises a cam (102) interconnected with the throttle shaft.

25. System according to claim 8, wherein the electromechanical controlmeans comprises a common electro-magnetic means responsive both to theamount of air flowing in the first path and further to said electricalsensing signal.

26. System according to claim 25, wherein the electro-mechanical meanscomprises control amplifier means and an electro-magnetic valve;

said valve forming the means controlling the flow of additional air andcomprising a valve seat (62);

a valve cone (63, 63) movable with respect to the valve seat;

magnet means (69) having an air gap;

and a coil adapted to move with respect to the air gap secured to thevalve cone, and connected to said control amplifier means.

27. System according to claim 26, wherein the air gap has an axiallynon-linear cross section.

28. System according to claim 25, wherein the electro-mechanical meanscomprises control amplifier means and an electromagnetic valve;

said valve forming the means controlling the flow of additional air andcomprising a valve seat (62); a valve cone (63) movable with respect tothe valve seat;

electro-magnetic means having an air gap;

an energizing coil (78) for said electromagnetic means;

and an armature adapted to move with respect to the air gap secured tothe valve cone (63), the energzing coil being connected to said controlamplifier.

29. System according to claim 28, wherein the air gap is toroidal andhas an axially non-linear cross section.

30. System according to claim 25, wherein the electro-mechanical meanscomprises a control amplifier means and an electro-magnetic valve, saidvalve forming the means controlling the flow of additional air andcomprising a valve seat (62);

a valve cone (63) movable with respect to the valve seat;

electro magnetic means controlling the movement of the valve cone andbeing connected to said control amplifier means.

3l. System according to claim 30, wherein the valve cone (63) has anon-linear side contour to provide a non-linear characteristic ofdisplacement with respect to flow through the valve.

32. System according to claim 30, comprising a guide rod (66) guidingthe movement of the valve cone (63);

a pair of leaf springs (85, 86) securing the guide rod in position inthe electromagnetic valve free from sliding friction.

33. System according to claim 30, wherein the electro-magnetic valve hasa magnet assembly (69);

a membrane (82) is located to seal the space between the magnet assembly(69) and the valve seat (62), the membrane being connected with themeans moving the valve cone by gas-tight connection;

and a pressure equalization opening bridging the membrane.

34. System according to claim 33, wherein a guide rod (66) is providedsecured to the valve cone and guiding the movement of the valve cone(63) of the electro-magnetic valve;

and wherein the pressure equalization opening comprises a central bore(81) in the guide rod bridging the region of the membrane and connectingboth sides of the membrane (82), the flow resistance of said borebridging the opening being high with respect to the flow resistance ofthe valve.

35. System according to claim 26, wherein the control amplifier meanscomprises a control amplifier (25) and a power amplifier (63) connectedto the output of the control amplifier;

the control amplifier being connected to the gas analysis means andproviding a signal representative of oxygen content in the exhaust gasto the power am plifier;

and additional signal input means are provided connected to at least oneof said amplifiers.

36. System according to claim 35, comprising transducer means (31)connected to the internal combustion engine and providing an enginecontrol output signal representative of engine controller position.

37. System according to claim 35, further comprising speed transducermeans (32, 33) connected to the internal combustion engine (11) andproviding a speed output signal representative of engine speed.

38. System according to claim 36, wherein the additional input signalmeans is connected to the engine control output signal.

39. System according to claim 36, wherein the additional signal inputmeans is connected to the speed output signal.

40. System according to claim 36, wherein the control amplifier (25) hastwo additional inputs, one additional input being connected to a commandsource (27) representative of a commanded air-fuel relationship (A);

- transducer means (31) are provided connected to the internalcombustion engine and providing an engine control output signalrepresentative of engine controller position, the engine control outputsignal being connected to the other additional input.

41. System according to claim 8, wherein the electromechanical controlmeans comprises a common electro-magnetic means responsive both to theamount of air flowing in the first path and further of said electricalsensing signal, said electro-magnetic means including control amplifiermeans and an elect'ro-magnetic valve, said valve forming the meanscontrolling the flow of air; said valve comprising a valve seat (62) anda valve cone (63) movable with respect to the valve seat;

cup-shaped magnetic means (69) having a toroidal air gap, and coil means(97) movable within the air p an operating rod (66) connected to saidcoil means,

the magnetic means being an electromagnet having an energizing coil(98), said energizing coil and the movable coil being controlled by saidcontrol amplifier means.

42. Systm according to claim 41, comprising a pair of power amplifiers(95, 96), one power amplifier each being connected to the movable coiland to said magnet coil;

and control circuit means controlling said power amplifiers forming saidcontrol amplifier means and comprising summing circuit means (90, 91,92) applying electrical voltages representative of said electricalsensing signal (23, 24) and of operating parameters (31; 32, 33) of theengine applied to one power amplifier and adding resistors (93, 94)being connected to the other power amplifier and having signalsrepresentative of operating parameters of the engine (31; 32, 33)applied thereto.

43. System according to claim 42, wherein the signals representative ofoperating parameters of the engine comprise signals representative of atleast one of: commanded engine controller position; engine speed.

44. System according to claim 8, wherein the exhaust gas analysis meanscomprises an oxygen sensor (23) including an oxygen ion conductive solideletrolyte and providing two surfaces, one surface being exposed to theexhaust gases from the engine and the other surface being exposed toambient air;

the surfaces having microporous platinum layers (43) applied thereto;

and contact means contacting the two platinum layers at the two sides ofthe solid electrolyte.

45. System according to claim 44, wherein the oxygen ion conductivesolid electrolyte comprises zirconium dioxide.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,759,232 Dated .September 18, 1973 Inventor(s) Josef WAHL et al (JosefWAHL and Peter Jflrgen SCHMIDT?) It is certified that error appears inthe above-identified patent and that said Letters Patent are herebycorrected as shown below:

l.Col. 1, line 16, change "are" to -is- 2.Claim 8, col. 13, line 47,change "a second"to -an additional. 3.Claim 8, col. 13, line 49, change"an" to--the-.-

Signed and sealed this 2nd day of April 197R.

(SEAL) Attest:

EDWARD PLFLE'IGHERJR. C. MARSHALL DANN Attesting Officer Commissioner ofPatents FORM PC3-1 0-6 uscoMM-Dc wan-P69 R 0.5. GOVERNMENT PRINTINGOFFICE: IBIS 0-365-33!

1. Method to remove polluting components from the exhaust gases ofinternal combustion engines comprising applying an air-fuel mixture tothe inlet manifold (12'') of the engine (11) over a first path (13);controlling (14) the relative proportion of air and fuel in the air-fuelmixture being admitted through said first path, in accordance with acommanded input (30); measuring the oxygen content (23) of the exhaustgases from the engine; applying air to the inlet manifold (12'') of theengine (11) over a second path (17); and controling (18) the amount ofair being admitted through the second path in accordance with a. theamount of air being admitted through the first path and, additionally,b. the measured oxygen content of the exhaust gases.
 2. Method accordingto claim 1 wherein the step of controlling the amount of air beingadmitted through the first path (13) comprises setting a throttle valve(14) in the main air duct in accordance with a commanded position; andthe step of controlling the amount of air being admitted through thesecond path (17) comprises providing an auxiliary air inlet duct (17),in shunt with the main air duct (14) and having an auxiliry valve (18);and controlling the position of the auxiliary valve (18) in accordancewith the position of the main throttle valve (14) as modified by themeasured oxygen content of the exhaust gases.
 3. Method according toclaim 1, wherein the step of controlling the amount of air beingadmitted through the second path comprises additionally controlling theAmount of air being admitted as a function of engine speed.
 4. Methodaccording to claim 1, wherein a control amplifier (25) is provided, andelectrically controlled air flow means are provided in said second path,the output of the control amplifier controlling the air flow controlmeans in the second path to effect the step of controlling the amount ofair flowing through the second path; and wherein the range of output ofthe control amplifier (25) is controlled by at least one of theparameters: engine speed; air flow in the first path.
 5. Methodaccording to claim 4, wherein the control amplifier (25) has a variabledelay time; and the delay between control input to the control amplifierand the control output thereof is varied in accordance with at least oneof the parameters: engine speed; air flow in the first path.
 6. Methodaccording to claim 1, wherein the air flow in the second path (17) iscontrolled such that the relationship of air mass to fuel being suppliedat the inlet manifold (12'') to the engine is just below thestoichiometric ratio and has a value of about 0.98.
 7. Method accordingto claim 5, comprising the step of after-burning unburned carbonmonoxide and hydrocarbons in a thermo reactor (19, 20), and thenreducing nitrogen-oxygen compounds in a catalytic reactor (21) followingthe thermo reactor.
 8. Internal combustion engine exhaust emissioncleaning system, in which the internal combustion engine (11) has aninlet manifold (12''), means (15) introducing fuel into the inletmanifold; means (14) controlling the flow of air in the inlet manifoldin a first path; means (17) introducing additional air into the inletmanifold in a second path; means (18) controlling the flow of additionalair into the inlet manifold through an additional air path; exhaust gasanalysis means (23) measuring the oxygen content of the exhaust gasesand deriving an electrical sensing signal; and electromechanical controlmeans connected to and controlling the flow control means for theadditional air, the electromechanical control means having an inputwhich is responsive to the amount of air flowing in the first path andfurther to said electrical sensing signal to control the flow ofadditional air as a function of the flow of air in the first path aswell as a function of a predetermined relationship of oxygen in theexhaust gas as sensed by said exhaust gas analysis means (23).
 9. Systemaccording to claim 8, wherein the internal combustion engine has asettable control (30) including means (31) deriving a signalrepresentative of the position of said control and applying said signalto the electromechanical control means in a direction to increaseresponse time of said control means when the settable control is set forhigh power operation of the engine providing for high air flow throughsaid first path.
 10. System according to claim 8, wherein the meanscontrolling the flow of air in the first path comprises a main throttlevalve (14) having a shaft (34); the flow control means for theadditional air path comprise an additional throttle valve (18) having anadditional shaft (29); and the electro-mechanical control meanscomprises mechanical means (38, 100) responsive to throttle shaft (34)deflection connected to operate the additional throttle shaft (29) andadditional electrical input position-output electrical signal transducermeans (35) responsive to the electrical sensing signal additionallydeflecting the additional throttle valve (18).
 11. System according toclaim 10, wherein the mechanical means comprises a bi-directionalone-way clutch (38) connected at the driven side with the main throttleshaft (34) and at the driving side to the additional throttle shaft (29)to transmit rotary movement from the throttle shaft, in both rotarydirections, to the additional throttle shaft (29) but not to transmitrotary movement in either rotational direction from the additionalthrOttle shaft (29) to the main throttle shaft (34); and the electricalinput-position output transducer comprises a synchro motor (35) and aslip coupling (37) connecting the synchro motor to the additionalthrottle shaft (29) to permit setting of the additional throttle (18)upon change in position of the main throttle shaft (34) and modifyingthis position under control of the operation of the synchro motor. 12.System according to claim 11, further comprising a closed servo loop(35, 36-39) including a position transducer (36) coupled to the outputshaft of the synchro motor (35).
 13. System according to claim 12,wherein the servo loop includes a servo amplifier (39) controlling theamount and direction of rotation of the synchro motor (35); and meansincluding a reference source (40) connected to the position transducer,the output from the position transducer forming a comparison input tothe servo amplifier (39).
 14. System according to claim 13, wherein theelectro-mechanical control means comprises a control amplifier (25)having an output connected to and controlling the servo amplifier (39);a source of command signals representative of commanded fuel-air ratio,said control amplifier having one input connected to said command sourceand another input connected to the output of the gas analysis means. 15.System according to claim 12, further comprising a position transducer(31) coupled to the main throttle shaft (34) to provide a signalrepresentative of main throttle shaft deflection.
 16. System accordingto claim 14, further comprising a position transducer (31) coupled tothe main control shaft (34) to provide a signal representatve of mainthrottle shaft deflection; said control amplifier having a third inputconnected to the output of the position transducer (31).
 17. Systemaccording to claim 14, wherein the control amplifier is an integratingamplifier.
 18. System according to claim 17, wherein the integratingamplifier (25) includes an operational amplifier (250) having an outputand an inverting input; and an integrating capacitor (251) connectedbetween the output and the inverting input.
 19. System according toclaim 18, (FIG. 9), wherein the gas analysis means (23) isinterconnected with the inverting input of the operational amplifier(250).
 20. System according to claim 18, further comprising a positiontransducer (31) coupled to the main throttle shaft (34) to provide asignal representative of main throttle shaft deflection; a firsttransistor (257) interconnecting the output of the position transducer(31) and the inverting input of the operational amplifier (250); aseries connection formed of an inverting amplifier (261) and a secondtransistor (258) connected in parallel to the first transistor; saidtransistors being of opposite conductivity types.
 21. System accordingto claim 20, further comprising a threshold switch (262, 263) connectedto the gas analysis means (23), the output of the threshold switch beingconnected to the base electrodes of the first and second transistors(257, 258).
 22. System according to claim 21, wherein the thresholdswitch comprises an operational amplifier (262) having a resistor (263)in the feedback circuit from the output to the non-inverting inputthereof.
 23. System according to claim 8, wherein the means (18)connecting the flow of additional air comprises a bypass valve having anelectro-mechanical positionable valve cone (63) and a mechanicallymovable valve seat (100); and drive means (102) operativelyinterconnecting the means controlling flow of air in the first path andthe mechanically movable valve seat to move the valve seat in accordancewith change in position of said flow control means.
 24. System accordingto claim 23, wherein the flow control means for the first path comprisesa throttle and a throttle shaft and the drive means comprises a cam(102) interconnected with the throttle shAft.
 25. System according toclaim 8, wherein the electro-mechanical control means comprises a commonelectro-magnetic means responsive both to the amount of air flowing inthe first path and further to said electrical sensing signal.
 26. Systemaccording to claim 25, wherein the electro-mechanical means comprisescontrol amplifier means and an electro-magnetic valve; said valveforming the means controlling the flow of additional air and comprisinga valve seat (62); a valve cone (63, 63'') movable with respect to thevalve seat; magnet means (69) having an air gap; and a coil adapted tomove with respect to the air gap secured to the valve cone, andconnected to said control amplifier means.
 27. System according to claim26, wherein the air gap has an axially non-linear cross section. 28.System according to claim 25, wherein the electro-mechanical meanscomprises control amplifier means and an electromagnetic valve; saidvalve forming the means controlling the flow of additional air andcomprising a valve seat (62); a valve cone (63) movable with respect tothe valve seat; electro-magnetic means having an air gap; an energizingcoil (78) for said electromagnetic means; and an armature adapted tomove with respect to the air gap secured to the valve cone (63), theenergzing coil being connected to said control amplifier.
 29. Systemaccording to claim 28, wherein the air gap is toroidal and has anaxially non-linear cross section.
 30. System according to claim 25,wherein the electro-mechanical means comprises a control amplifier meansand an electro-magnetic valve, said valve forming the means controllingthe flow of additional air and comprising a valve seat (62); a valvecone (63) movable with respect to the valve seat; electro-magnetic meanscontrolling the movement of the valve cone and being connected to saidcontrol amplifier means.
 31. System according to claim 30, wherein thevalve cone (63) has a non-linear side contour to provide a non-linearcharacteristic of displacement with respect to flow through the valve.32. System according to claim 30, comprising a guide rod (66) guidingthe movement of the valve cone (63); a pair of leaf springs (85, 86)securing the guide rod in position in the electro-magnetic valve freefrom sliding friction.
 33. System according to claim 30, wherein theelectro-magnetic valve has a magnet assembly (69); a membrane (82) islocated to seal the space between the magnet assembly (69) and the valveseat (62), the membrane being connected with the means moving the valvecone by gas-tight connection; and a pressure equalization openingbridging the membrane.
 34. System according to claim 33, wherein a guiderod (66) is provided secured to the valve cone and guiding the movementof the valve cone (63) of the electro-magnetic valve; and wherein thepressure equalization opening comprises a central bore (81) in the guiderod bridging the region of the membrane and connecting both sides of themembrane (82), the flow resistance of said bore bridging the openingbeing high with respect to the flow resistance of the valve.
 35. Systemaccording to claim 26, wherein the control amplifier means comprises acontrol amplifier (25) and a power amplifier (63) connected to theoutput of the control amplifier; the control amplifier being connectedto the gas analysis means and providing a signal representative ofoxygen content in the exhaust gas to the power amplifier; and additionalsignal input means are provided connected to at least one of saidamplifiers.
 36. System according to claim 35, comprising transducermeans (31) connected to the internal combustion engine and providing anengine control output signal representative of engine controllerposition.
 37. System according to claim 35, further comprising speedtransducer means (32, 33) connected to the internal combustion engine(11) and providing a speed output signAl representative of engine speed.38. System according to claim 36, wherein the additional input signalmeans is connected to the engine control output signal.
 39. Systemaccording to claim 36, wherein the additional signal input means isconnected to the speed output signal.
 40. System according to claim 36,wherein the control amplifier (25) has two additional inputs, oneadditional input being connected to a command source (27) representativeof a commanded air-fuel relationship ( lambda ); transducer means (31)are provided connected to the internal combustion engine and providingan engine control output signal representative of engine controllerposition, the engine control output signal being connected to the otheradditional input.
 41. System according to claim 8, wherein theelectro-mechanical control means comprises a common electro-magneticmeans responsive both to the amount of air flowing in the first path andfurther of said electrical sensing signal, said electro-magnetic meansincluding control amplifier means and an electro-magnetic valve, saidvalve forming the means controlling the flow of air; said valvecomprising a valve seat (62) and a valve cone (63) movable with respectto the valve seat; cup-shaped magnetic means (69) having a toroidal airgap, and coil means (97) movable within the air gap; an operating rod(66) connected to said coil means, the magnetic means being anelectromagnet having an energizing coil (98), said energizing coil andthe movable coil being controlled by said control amplifier means. 42.System according to claim 41, comprising a pair of power amplifiers (95,96), one power amplifier each being connected to the movable coil and tosaid magnet coil; and control circuit means controlling said poweramplifiers forming said control amplifier means and comprising summingcircuit means (90, 91, 92) applying electrical voltages representativeof said electrical sensing signal (23, 24) and of operating parameters(31; 32, 33) of the engine applied to one power amplifier and addingresistors (93, 94) being connected to the other power amplifier andhaving signals representative of operating parameters of the engine (31;32, 33) applied thereto.
 43. System according to claim 42, wherein thesignals representative of operating parameters of the engine comprisesignals representative of at least one of: commanded engine controllerposition; engine speed.
 44. System according to claim 8, wherein theexhaust gas analysis means comprises an oxygen sensor (23) including anoxygen ion conductive solid eletrolyte and providing two surfaces, onesurface being exposed to the exhaust gases from the engine and the othersurface being exposed to ambient air; the surfaces having microporousplatinum layers (43) applied thereto; and contact means contacting thetwo platinum layers at the two sides of the solid electrolyte. 45.System according to claim 44, wherein the oxygen ion conductive solidelectrolyte comprises zirconium dioxide.